Patent application title: OPTICAL DEVICE, IN PARTICULAR FOR AN AUTOMOTIVE VEHICLE, SUCH AS A LIGHTING OR SIGNALING DEVICE

Abstract:

An optical device, in particular for an automotive vehicle, such as a
lighting or signaling device, comprising at least one light source, and
at least one light guide designed to guide at least some of the light
emitted by the light source, the light guide comprising at least one
output face and at least one reflection face designed to reflect, towards
the output face, light being propagated in the guide, wherein the light
guide exhibits a cylindrical sheet form and/or the output face is not
completely planar.

Claims:

1. An optical device, in particular for an automotive vehicle, such as a
lighting or signaling device, comprising:at least one light source; andat
least one light guide designed to guide at least some of the light
emitted by said at least one light source, said at least one light guide
comprising at least one output face and at least one reflection face
designed to reflect, towards said at least one output face, light being
propagated in said at least one light guide;wherein said at least one
light guide exhibits a cylindrical sheet form.

2. The optical device according to claim 1, wherein said at least one
output face is contained in a three dimensional surface, in particular
different from a sphere.

3. The optical device according to claim 1, wherein said at least one
output face is designed to diffuse the light leaving said at least one
output face, in particular using flutes on said at least one output face.

4. The optical device according to claim 1, wherein said at least one
reflection face of said at least one light guide is included in a ruled
surface described by straight lines perpendicular to a longitudinal axis
(X) of the cylindrical sheet.

5. The optical device according to claim 1, wherein said at least one
reflection face is included in two ruled surfaces which intersect in
particular while forming at the intersection an angle varying between
70.degree. and 110.degree., and in particular close to 90.degree..

6. The optical device according to claim 1, wherein said at least one
light guide is monolithic, in particular by molding a plastic material.

7. The optical device according to claim 1, wherein said at least one
light guide comprises at least one input cavity for the light, said at
least one input cavity in particular being designed to receive said at
least one light source at least partially.

8. The optical device according to claim 1, wherein said at least one
light guide is designed so that a light beam issuing from said at least
one output face is substantially parallel to an optical axis of said
optical device.

9. The optical device according to claim 1, wherein said at least one
light source comprises at least one LED, in particular an LED with radial
radiation.

10. The optical device according to 1, wherein said at least one light
guide is extended, on the side of its output face, by a portion guiding
the light which exhibits a cylindrical sheet form or otherwise.

11. An optical device, in particular for an automotive vehicle, such as a
lighting or signaling device, comprising:at least one light source; andat
least one light guide designed to guide at least some of the light
emitted by said at least one light source, said at least one light guide
comprising at least one output face and at least one reflection face
designed to reflect, towards said at least one output face, light being
propagated in said at least one light guide;wherein said at least one
output face of said at least one light guide is not completely planar.

12. A light guide designed to guide at least some of the light emitted by
a light source, said light guide comprising:at least one output face;
andat least one reflection face designed to reflect, towards said at
least one output face, light being propagated in said light guide, this
said light guide exhibiting a cylindrical sheet form.

13. A process for manufacturing a light guide, said light guide being
designed to guide at least some of the light emitted by a light source,
said light guide comprising at least one output face and at least one
reflection face designed to reflect, towards said at least one output
face, light being propagated in said light guide, said light guide
exhibiting an optical axis and at least one output face exhibiting a
predetermined shape, the process comprising the following steps of:a)
obtaining a geometrical cylindrical sheet contour parallel to each other
by extruding said at least one output face of said optical axis;b)
carrying out a geometrical operation so as to unfold said cylindrical
sheet contour and making it planar;c) obtaining, for this geometrical
unfolded sheet contour, a reflection face shape;d) obtaining a
cylindrical sheet form according to said reflection face shape; ande)
manufacturing, in particular by molding a plastic material, said light
guide with said cylindrical sheet form obtained.

14. The process according to claim 13, wherein said unfolded sheet contour
obtained in step b) exhibits an unfolded output face in particular with a
planar contour.

15. The process according to claim 13, wherein in step c), the contour of
said at least one reflection face is obtained on the basis of a planar
profile of said at least one output face obtained in the step c/, by
considering preservation of an optical path on said at least one
reflection face.

16. The optical device according to claim 2, wherein said at least one
output face is designed to diffuse the light leaving said at least one
output face, in particular using flutes on said at least one output face.

17. The optical device according to claim 2, wherein said at least one
reflection face of said at least one light guide is included in a ruled
surface described by straight lines perpendicular to a longitudinal axis
(X) of the cylindrical sheet.

18. The optical device according to claim 3, wherein said at least one
reflection face of said at least one light guide is included in a ruled
surface described by straight lines perpendicular to a longitudinal axis
(X) of the cylindrical sheet.

19. The optical device according to claim 2, wherein said at least one
reflection face is included in two ruled surfaces which intersect in
particular while forming at the intersection an angle varying between
70.degree. and 110.degree., and in particular close to 90.degree..

20. The optical device according to claim 3, wherein said at least one
reflection face is included in two ruled surfaces which intersect in
particular while forming at the intersection an angle varying between
70.degree. and 110.degree., and in particular close to 90.degree..

Description:

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001]This application claims priority to French Application No. 0900507
filed Feb. 5, 2009, which application is incorporated herein by reference
and made a part hereof.

BACKGROUND OF THE INVENTION

[0002]1. Field of the Invention

[0003]The invention relates to an optical device, in particular for an
automotive vehicle, such as a lighting or signaling device.

[0004]2. Description of the Related Art

[0005]A lighting or signaling device for an automotive vehicle is known
from patent application EP 1 881 263, which is equivalent to U.S. Patent
Publication 2008/0019139 which is incorporated herein by reference and
made a part hereof, of the applicant. The lighting device can emit a
light beam "F" according to a longitudinal optical axis "A". This
lighting device comprises at least one sheet for guiding the light, at
least part of which appears as a portion of a spherical segment.

[0006]The guide sheet is thus delimited, in the direction of the
thickness, by two guide faces substantially parallel to each other on at
least some of the sheet.

[0007]The guide sheet is delimited laterally by a front output section for
the light rays and by a rear reflection section for the light. The ends
of the reflection section are directly connected to the ends of the
output section so as to form the outer contour of the guide sheet.

[0008]The contour of the output section for the light forms a planar arc
of a circle. The guide sheet comprises an input opening for the light in
the sheet.

[0009]A light source is arranged in the opening close to or in contact
with the input section for the light rays.

[0010]The light source can emit light rays according to a globally radial
direction around a source axis "S" which is normal to the guide sheet.
More precisely, the light source can radially emit a fan of light rays at
least in the direction of the reflection section.

[0011]The guide sheet is made of a transparent material whose index of
refraction is higher than the index of refraction of the medium in which
the lighting device is intended to be immersed, air for example. Thus, a
light ray introduced into the thickness of the sheet through its input
section meets the higher or lower guide faces at an angle of incidence
relative to the normal "N" which is higher than a limit angle of
refraction. The ray can then be completely reflected by the guide faces.

[0012]The light ray is thus guided into the thickness of the guide sheet
by successive reflections between the two guide faces.

[0013]The incidental light rays which emerge at the rear are intended to
be reflected by the reflection section, then the light rays thus
reflected are directed towards the output section. The reflected light
rays thus emerge through the output section.

[0014]The light source is an light emitting diode or "LED" known as "side
emitter" which emits light rays in an essentially perpendicular direction
to the source axis "5".

[0015]The light source can also consist of an incandescent lamp, for
example a halogen lamp, with an axial filament, inserted in the contour
delimited by the input section. Advantageously it may be proposed in this
case that a zone of the guide sheet, close to the input section, is made
of glass, although the remainder of the sheet is made of plastic material
molded onto this zone of glass. Such a design enables the thermal
problems which the use of an incandescent light source might generate to
be surmounted.

[0016]In the device described above the output section, or output face,
exhibits a generally planar shape, with a general profile in the form of
an arc of a circle.

[0017]A device with a guide sheet is known from patent application EP 1
992 868.

[0018]The above configurations correspond in particular to circular or
annular profiles, and the guide zone near the source is close to a
spherical portion.

[0019]There exists in particular a need, especially at the request of
automotive manufacturers, for a light guide essentially of the type
described above, which exhibits an output face having any arbitrary form,
in particular a non-planar shape, extending either in a plane
perpendicular to the optical axis or in a plane containing the optical
axis.

SUMMARY OF THE INVENTION

[0020]The invention notably aims at fulfilling this need.

[0021]One object of the invention is therefore an optical device, in
particular for an automotive vehicle, such as a lighting or signaling
device, comprising:

[0022]at least one light source;

[0023]at least one light guide designed to guide at least some of the
light emitted by the light source, the light guide comprising at least
one output face and at least one reflection face designed to reflect,
towards the output face, light being propagated in the guide;

[0024]wherein the light guide exhibits a cylindrical sheet form.

[0025]In the present invention, a cylinder designates a surface in the
space, defined by a straight line, called generatrix, on the one hand
passing through a variable point following a closed or open curve, known
as directrix curve, and on the other hand maintaining a fixed direction.

[0026]A sheet designates a solid exhibiting two principal faces, planar or
curved, which are substantially parallel to each other and the thickness
of this solid, measured between the two principal faces, is substantially
less than dimensions, such as length or width, of these principal faces.

[0027]The cylindrical sheet according to the invention is preferably
non-planar.

[0028]The construction of the optical device according to the invention
enables a light guide with an output face exhibiting any arbitrary shape
to be obtained, which meets the automotive manufacturers' requirements.

[0029]This construction in particular provides a light guide with an
output face having a shape which could not be obtained using a spherical
segment light guide, such as described in patent application EP 1 881
263, which is equivalent to U.S. Patent Publication 2008/0019139,
mentioned above.

[0030]In an illustrative embodiment of the invention, the output face of
the light guide is different from a planar portion, that is to say this
output face is not entirely contained in one plane.

[0031]If desirable, the output face is contained in a three dimensional
surface, in particular different from a sphere.

[0032]This output face can be included in a ruled surface or,
alternatively, in whatever non-ruled surface.

[0033]The term "ruled surface" means a surface through each point of which
a straight line contained in the surface passes.

[0034]If necessary, the output face is designed to diffuse the light
emerging from this output face, in particular by means of flutes on this
output face.

[0035]The output face can exhibit a closed or open annular form.

[0036]In an illustrative embodiment of the invention, the reflection face
of the light guide is included in a ruled surface described by straight
lines, perpendicular to the longitudinal axis of the cylindrical sheet.

[0037]Alternatively, the reflection face is included in two ruled surfaces
which intersect in particular forming at the intersection an angle
varying between 70° and 110°, and in particular near to
90°.

[0038]The reflection face can exhibit a closed or open annular form.

[0039]The light guide can be monolithic, being made of a single block, for
example by molding a plastic material.

[0040]In an illustrative embodiment of the invention, the light guide
comprises at least one input cavity for the light, this cavity in
particular being designed to receive the light source at least partially.
This cavity preferably opens onto at least one of the principal faces of
the light guide, and not for example onto a rear section of this sheet.

[0041]Possibly, this cavity is traversing.

[0042]If necessary, the light source remains on the surface of the light
guide.

[0043]If desirable, the device comprises a plurality of light sources
designed to illuminate the light guide.

[0044]In an illustrative embodiment of the invention, the device is
designed, through the output face of the light guide, to emit light with
a luminous intensity ranging between 50 candelas and 1000 candelas.

[0046]For example the guide light has a thickness ranging between 2 mm and
6 mm, in particular between 3 mm and 5 mm.

[0047]If necessary, the reflection face, at least over part of its length,
can be aluminized.

[0048]Alternatively, the rear reflection face is designed to allow
reflection of the light being propagated in the guide by simple or double
total reflection.

[0049]This double total reflection results in particular if the reflection
face is included in two ruled surfaces which intersect.

[0050]Preferably, the light guide is designed so that the light beam
emerging from the output face is substantially parallel to the optical
axis of the device so that illumination issuing from the guide appears
substantially homogeneous.

[0051]For example, the light source comprises at least one LED, in
particular an LED with radial radiation.

[0052]If desirable, the device comprises a plurality of light guides
arranged side by side.

[0053]In an illustrative embodiment of the invention, the light guide is
extended, from the side of its output face, by a portion guiding the
light which not necessarily exhibits the form of a cylindrical sheet.

[0054]The object of the invention is also an optical device, in particular
for an automotive vehicle, such as a lighting or signaling device,
comprising:

[0055]at least one light source;

[0056]at least one light guide designed to guide at least some of the
light emitted by the light source, the light guide comprising at least
one output face and at least one reflection face designed to reflect,
towards the output face, light being propagated in the guide;

[0057]wherein the output face of the light guide is not completely planar.

[0058]Yet another object of the invention is a light guide designed to
guide at least some of the light emitted by a light source, the light
guide comprising at least one output face and at least one reflection
face designed to reflect, towards the output face, light being propagated
in the guide, this light guide exhibiting a cylindrical sheet form.

[0059]The invention also relates to a manufacturing process of a light
guide, this light guide being designed to guide at least some of the
light emitted by a light source, the light guide comprising at least one
output face and at least one reflection face designed to reflect, towards
the output face, light being propagated in the guide, this light guide
exhibiting an optical axis, the output face having an imposed
predetermined shape, the process comprising the following steps of:

[0061]b) carrying out a geometrical operation so as to unfold the
cylindrical sheet contour and making it planar;

[0062]c) obtaining, for this geometrical unfolded sheet contour, a shape
of the reflection face(s);

[0063]d) obtaining the cylindrical sheet form (in three dimensions)
depending on the shape of the reflection face and

[0064]e) manufacturing, in particular by molding a plastic material, the
light guide with the cylindrical sheet form obtained.

[0065]In an illustrative embodiment of the invention, the unfolded sheet
contour obtained in step b) can exhibit an unfolded output face with a
planar contour, this unfolded output face being obtained depending on the
output face imposed.

[0066]In step c), the contour of the reflection face is obtained on the
basis of a planar profile of the contour of the output face obtained
previously, by considering preservation of the optical path on the
reflection face.

[0067]According to the invention, the entire sheet can be cylindrical or
correspond to a ruled surface.

[0068]The output face can be a complex 3D curve not included in a plane or
a sphere.

[0069]The ruled surface property of the sheet can appear in particular
around to the light source.

[0070]The invention permits guides with a relatively complex profile to be
created.

[0071]According to the invention, the guide can be made by extrusion.

[0072]These and other objects and advantages of the invention will be
apparent from the following description, the accompanying drawings and
the appended claims.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

[0073]The invention can be better understood on reading the following
detailed description of non-restrictive illustrative embodiments of the
invention and on examining the appended drawing, wherein:

[0074]FIG. 1 illustrates, schematically and partially, in perspective, an
optical device according to an illustrative embodiment of the invention;

[0075]FIG. 2 shows, schematically and partially, according to a transverse
section along II-II, the device in FIG. 1;

[0076]FIG. 3 illustrates, schematically and partially, the path of a light
ray reflected on the reflection face of the light guide of the device in
FIG. 1;

[0078]FIG. 5 illustrates, schematically and partially, the principle of
calculating the profile of the reflection face of the guide in FIG. 1;

[0079]FIG. 6 shows, schematically and partially, a light guide according
to another illustrative embodiment of the invention; and

[0080]FIG. 7 shows, schematically and partially, an optical device with
two light guides side by side, according to another illustrative
embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0081]FIGS. 1 and 3 feature an optical device 1 for an automotive vehicle,
such as a lighting or signaling device, comprising:

[0082]a light source 2 formed by an LED with radial radiation;

[0083]a light guide 3 designed to guide some of the light emitted by the
light source 2, the light guide 3 comprising at least one output face 5
and at least one reflection face 6 designed to reflect, towards the
output face 5, light L being propagated in light guide 3.

[0084]The light guide 3 exhibits the form of a non-planar cylindrical
sheet with the longitudinal axis X and two non-planar principal faces 10
and 11, which are substantially parallel to each other.

[0085]In the example described, the cylindrical sheet is open, that is to
say it has not closed again on itself around the longitudinal axis X.

[0086]The thickness of this light guide 3, measured between the two
principal faces 10 and 11, for example ranges between 3 mm and 5 mm.

[0087]FIG. 1, for better clarity of the drawing, shows the intersections
(dotted lines C1 and C2) between two planes R1 and R2 (perpendicular to
the longitudinal axis X) with the cylindrical sheet.

[0088]The output face 5 of the light guide 3 is different from a planar
portion, that is to say this output face 5 is not entirely contained in
the plane R2.

[0089]In particular, this output face 5 is contained in a three
dimensional surface different from a sphere.

[0091]In addition the reflection face 6 of the light guide 3 is included
in a ruled surface described by straight lines, perpendicular to the
cylindrical sheet.

[0092]Alternatively, the reflection face 6 can be included in two ruled
surfaces which intersect in particular forming at the intersection an
angle varying between 70° and 110°, and in particular near
to 90°.

[0093]In the example described, the light guide 3 is monolithic, being
made of a single block, for example by molding a plastic material with an
index of refraction n.

[0094]The plastic material used for example can be PMMA with an index of
refraction 1.49 or PC with an index of refraction 1.59.

[0095]The reflection face 6, at least over a portion of its length, can be
aluminized or, alternatively, the latter is designed to allow reflection
of the light being propagated in light guide 3 by simple or double total
reflection.

[0096]As illustrated in FIG. 2, the light guide 3 comprises an input
cavity 12 for the light, this cavity 12 being designed to receive the
light source 2 at least partially.

[0097]This cavity 12, which is traversing, opens onto the principal faces
10 and 11 of the light guide 3.

[0098]In the example described, optical device 1 is designed, through the
output face 5 of the light guide 3, to emit a light of luminous intensity
ranging between 50 candelas and 1000 candelas.

[0099]The light guide 3 is designed so that the light beam resulting from
the output face 5 is substantially parallel to the optical axis A of the
optical device 1 so that illumination issuing from the light guide 3
appears substantially homogeneous and so that on average the rays are
directed along the optical axis A.

[0100]In the example described, the optical axis A and the longitudinal
axis X are merged.

[0101]The process for manufacturing the light guide 3 will now be
described in detail.

[0102]It should be noted that this process aims at obtaining a light guide
3 with a predetermined output face 5, the three dimensional shape of
which is imposed for example by one automotive manufacturer.

[0103]As will be seen below, the process comprises a major step of
determining the shape of the reflection face 6 which is adapted with
respect to the imposed output face 5, so that the output face 5 is seen
in a homogeneous way and so that the rays emerging from the output face
5, on average, leave it according to the direction of the optical axis A.

[0106]b) carrying out a geometrical operation so as to unfold cylindrical
sheet contour 20 and making it planar;

[0107]c) obtaining, for this geometrical unfolded sheet contour 20, the
shape of the reflection face 6;

[0108]d) obtaining the cylindrical sheet form (in three dimensions)
according to the shape of the reflection face 6; and

[0109]e) manufacturing, by molding a plastic material, the light guide 3
with the cylindrical sheet form obtained.

[0110]In the example described, unfolded sheet contour 20 obtained in step
b) can exhibit an unfolded output face 5a with a planar contour, this
planar unfolded output face 5a being obtained on the basis of the imposed
output face 5.

[0111]This unfolded output face 5a with a planar contour can be obtained
in the following way.

[0112]Let us consider the optical axis A, (Oi) a horizontal axis and (Ok)
a vertical axis, and a point M of coordinates (x, y, z) of the contour of
the imposed output face 5

[0113]The contour of the unfolded output face 5a is calculated in the
following way.

[0114]Let us consider a point M' of this contour.

[0115]This point M' of coordinates (x', y', z'), image of the point M, is
determined as follows.

[0116]z'=0

[0117]y'=y

[0118]x' is calculated on the basis of the curvilinear x-coordinate of the
projection of the three dimensional profile of the imposed output face 5
on a plane perpendicular to optical axis A.

[0119]Once contour 20 of the sheet has been unfolded and the contour of
the unfolded output face 5a has been determined, the planar reflection
face 6a (see FIG. 5) is calculated using the principle of preserving the
optical path on the reflection face 6a.

[0120]With reference to FIG. 5, this principle corresponds to the fact
that the optical path between the light source 2 and output wave surface
22 is constant, namely

n*(LP1)+n*(P1H1)+(H1K1)=n*(LP2)+n*(P2H2)+(H2K2)=constant

[0121]P1 and P2 are points of the unfolded planar reflection face 6a, H1
and H2 points of the unfolded output face 5a, K1 and K2 points of the
wave surface 22, and L a point designating the light source 2.

[0122]Determining the profile of the unfolded planar reflection face 6a
amounts to finding the place described by points P1, P2.

[0123]The applicant has noted that this method is particularly effective
and enables satisfactory results to be obtained quickly.

[0124]Then the sheet with the contour of the reflection face 6 is
reconstructed and adapted by carrying out a geometrical operation of
folding the sheet in the following way.

[0125]After step c) the contour of the reflection face 6 which intersects
the sheet is obtained. Folding the sheet (step d)) results in the contour
in question.

[0126]The three dimensional reflection face 6 is constructed as one or
more ruled surfaces which are based on the new contour.

[0127]Let us consider P of coordinates (x, y, z) a point of the contour of
the planar reflection face 6a and P' of coordinates (x', y', z') a point
of the contour of the final reflection face 6 on the sheet known as
`real`.

[0128]Therefore:

[0129]y'=y

[0130]and x' and z' are calculated by considering the point associated
with the front profile.

[0131]The profile of the reflection face 6 is calculated for the `real`
sheet in three dimensions by constructing this rear reflection face 6 so
that it is included in a ruled surface made up of all the segments of
straight lines perpendicular to the sheet at any point of the profile of
the reflection face 6.

[0132]In one case, the ruled surface is defined with all the normals to
the sheet which pass through the contour.

[0133]Alternatively, two surfaces defined by straight lines passing
through the contour and forming an angle of 90° relative to each
other, the bisectrix of the two straight lines being tangent to the
sheet, are created.

[0134]Of course, the invention is not limited to the illustrative
embodiment which has just been described.

[0135]For example, as illustrated in FIG. 6, the light guide 3 can
comprise several petals 25 placed end to end, enabling a light guide 3 of
large dimensions to be created while preserving a reasonable depth.

[0136]Moreover, this enables functions with a strong intensity to be
obtained by using several LEDs each having a relatively low flux.

[0137]For example again, as illustrated in FIG. 7, the optical device 1
can comprise two light guides 3 arranged in an adjacent way.

[0138]While the method herein described, and the forms of apparatus for
carrying this method into effect, constitute preferred embodiments of
this invention, it is to be understood that the invention is not limited
to this precise method and forms of apparatus, and that changes may be
made in either without departing from the scope of the invention, which
is defined in the appended claims.